diff --git a/ChangeLog b/ChangeLog
index 3d006ffeee..df76363978 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Aug  7 17:40:24 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* mkconfig.rb, lib/rbconfig/obsolete.rb: warn obsolete and
+	  deprecated Config.
+
 Sat Aug  7 17:18:34 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/extmk.rb (extract_makefile): follow the change of
diff --git a/lib/rbconfig/obsolete.rb b/lib/rbconfig/obsolete.rb
new file mode 100644
index 0000000000..fcc7151ad2
--- /dev/null
+++ b/lib/rbconfig/obsolete.rb
@@ -0,0 +1,2 @@
+warn "Use RbConfig instead of obsolete and deprecated Config."
+Config = RbConfig # compatibility for ruby-1.8.4 and older.
diff --git a/tool/mkconfig.rb b/tool/mkconfig.rb
index ac24821829..07d6982701 100755
--- a/tool/mkconfig.rb
+++ b/tool/mkconfig.rb
@@ -213,7 +213,7 @@ print <<EOS
     )
   end
 end
-Config = RbConfig # compatibility for ruby-1.8.4 and older.
+autoload :Config, "rbconfig/obsolete.rb" # compatibility for ruby-1.8.4 and older.
 CROSS_COMPILING = nil unless defined? CROSS_COMPILING
 EOS